I have been trying to calculate the excitation energies of small polyaromatic hydrocarbon molecules like naphthalene, pyrene etc using the Tamm-Dancoff approximation via the TD-DFT module.

My first benchmark was with the naphthalene cation, for which I managed to reproduce available TD-DFT data from the literature.

In the case of neutral molecules, all of my attempts failed to compare with any literature data.

My calculation steps are the following:
1. Optimize the geometry of the neutral molecule with tight convergence criteria using odft and mult=1.
2. Retrieve the final geometry and movecs file and use them in a TD-DFT calculation.